During vitreoretinal surgery, the surgeon views the interior of the eye through the patient's cornea and lens. Because the interior of the eye is the portion on which the surgical procedure is being performed, it is critical that a vitreoretinal surgeon be able to see into the eye at all times during surgery.
In order to repair a rhegmatogenous detachment of the retina (in which the neurosensory retina is torn or cut, allowing fluid to collect underneath it), the surgeon first removes the vitreous humor (or any other liquid or gas in the eye) and fills the eye with balanced saline solution, for example. The surgeon then performs a fluid-gas exchange procedure in which the saline solution is removed at the same volumetric rate as a gas (usually sterile air from the operating room) is injected. As the gas replaces the fluid, any subretinal fluid is squeezed from under the retina and readily removed with an extrusion cannula. Once all the saline solution is removed, the surgeon seals the retinal hole, tear, or cut with endolaser photocoagulation, for example, and either leaves the air in the eye or replaces the gas with a tamponade of silicone oil or a long-lasting inert gas like C.sub.3 F.sub.8 or SF.sub.6.
The surgeon's vision is often impaired during the fluid-gas exchange by water or silicone droplets that condense on the posterior surface of the lens in (or just posterior to) the anterior chamber of the eye. This condensation can make it difficult or impossible to see and repair the retinal detachment. Other cases have been reported in which the condensation persists post-operatively and impairs the patient's vision.
The formation of condensation during the fluid-gas exchange portion of the vitrectomy is particularly common and troublesome on the posterior surface of silicone lenses in eyes on which a capsulotomy has been performed. The results of one study published in the May 1995 issue of Ophthalmology at pages 733-36 indicated that condensation occurred in 11 of 11 patients who had a silicone lens and a capsulotomy. The same study indicated that no condensation occurred in 7 of 7 patients who had silicone lenses without a capsulotomy.
Various methods of removing water condensation from silicone lenses have been tried, with limited success. In the May 1995 study discussed above, attempts to remove the condensation with a soft-tipped aspiration cannula partially cleared the condensation in 6 of the 11 patients in which condensation occurred, but the condensation quickly reappeared to completely obscure the surgeon's vision after only one to two minutes. The May 1995 study also suggested that water condensation might be more effectively removed by applying a thin film of silicone oil to the lens. However, the film has been found to coalesce into silicone droplets on the lens surface. These silicone droplets significantly impaired the surgeon's vision into the eye and were even more difficult to remove than water condensation. Others have reported that a fluid-gas exchange performed on a patient's eye previously filled with silicone oil and having a silicone lens resulted in inoperative silicone condensation that could not be removed. Therefore, this method has been found appropriate only in those patients in which the eye will be filled with silicone oil as a long-term tamponade. The authors of the May 1995 study have recommended, however, that the silicone oil tamponade be used only as a last resort, when other approaches have failed.
Doctors Sappenfield, Cohen, and Gitter described another approach to clearing water condensation from the lens in the July 1989 issue of the American Journal of Ophthalmology. Sappenfield et al. suggested inserting an angled cannula through the sclerotomy and injecting a balanced salt solution onto the posterior surface of the lens. This approach was reported to have successfully removed the water condensation in one particular case, but it requires injection of fluid into an eye from which the surgeon is trying to remove fluid. Adding fluid in this manner delays and thus impairs the fluid-gas exchange.
Sappenfield et al. also suggested warming lens using the intraocular irrigating solution (which fills the eye before the fluid-gas exchange portion of the vitrectomy) or introducing a small amount of viscoelastic material (e.g., hyaluronic acid) onto the posterior surface of the lens. It has also been suggested that filling the anterior chamber of the eye with warm viscoelastic fluid would warm the lens sufficiently to prevent condensation. While these approaches may succeed in temporarily clearing water condensation, they require constant manipulation of the instruments that deliver irrigation solution and leave a film of fluid on the posterior lens that distorts the surgeon's view into the eye. Thus, retinal surgeons commonly believe that using warm irrigation solutions or depositing viscoelastic fluids on the posterior lens is at best a temporary and unsatisfactory method of clearing water condensation that requires added and unwanted manipulation of instruments during surgery.
Condensation has also been observed during the fluid-gas exchange procedure on the posterior surface of other types of artificial lenses including polymethylmethacralate (PMMA), acrylic, hydragel, and heparin-coated PMMA lenses. While water condensation on these lenses has not been reported to be as widespread or persistent a problem, the proposed solutions for preventing and clearing water condensation from silicone lenses are not completely effective on these other lenses. Thus, a need continues to exist for a quick, simple, and long-lasting method for removing water condensation during the fluid-gas exchange portion of a pars plana vitrectomy from the posterior surface of an artificial lens.